Several techniques exist for densifying a fiber texture with a matrix of alumina, in particular techniques that make use of a liquid.
One known method consists in impregnating the fiber texture on successive occasions with a liquid composition that constitutes a precursor of alumina. After each impregnation, the texture is dried and subjected to heat treatment to convert the precursor into alumina. That method has the drawback of being lengthy and expensive to implement. It is usually necessary to perform numerous consecutive cycles of impregnation-drying-heat treatment to achieve the desired degree of densification.
Another known method, described in particular in Document FR-A-2 526 785 consists in sucking a very fine powder of alumina in suspension in a liquid through the fiber texture. After being infiltrated with alumina powder, the texture is dried and is subjected to sintering heat treatment. That technique of is applicable only to making parts that are small in size and simple in shape. In addition, the grains of alumina within the matrix are bonded together only weakly.
In Document FR-A-2 091 419, a method is described comprising impregnating fibrous zirconia with a liquid containing zirconia powder and a liquid precursor of zirconia. The fibrous zirconia impregnated in this way is deposited on a metal part that is coated with a porcelain enamel, and the entire assembly is dried and heated. Once those operations have been performed, a metal part is obtained which is coated with zirconia and which can be used with success in environments that are hot and corrosive; the method used achieving a good metal-ceramic bond.
Another technique is described in Document EP-A-0 130 105. It consists initially in impregnating a three-dimensional (3D) texture of refractory fibers with a suspension of ceramic powder in a liquid containing a very small quantity of a resin (polyvinyl alcohol). After drying, the ceramic grains occupy the larger pores of the 3D texture (filling of the macropores). In order to densify the material completely, the 3D texture with its ceramic grains is impregnated by means of a liquid precursor of a ceramic so as to fill the micropores. The part is then subjected to heat treatment to transform the liquid precursor into ceramic and to eliminate the resin. The latter operations of impregnation and heat treatment are repeated several times. That method makes it possible to densify a 3D fiber texture relatively quickly without using pressure.
An object of the present invention is to provide an improved method enabling a fiber reinforcing texture to be densified with an alumina matrix by using a liquid.